"Since 2010 it's likely that Metallica have lost more money than they've made," the biographers write in the two-volume biography on the band, "Birth School Metallica Death" and "Into the Black". In their interview with The Weeklings, they continue to list previous ventures that are leaving the band in the red.

In particular, they mention the band's Orion festivals that are now defunct, plus their Through the Never concert film, which they claim will only make back a small portion of its $32 million budget.

"By their own admission, the two stagings of the Orion festival were disastrous financially, and the shambles that was the Through The Never movie cost $32 million and will only recoup a fraction of that amount," they say in the interview.

"Factor in HQ staff salaries, crew retainers and assorted running costs associated with maintaining an entertainment corporation and you can easily understand why the band - of necessity now rather than by choice - are driven to tour Europe every summer.